1. Field of the Invention
The present invention relates generally to fan blade retainers that are disposed across dovetail slots in gas turbine engine assemblies and, more particularly, to such retainers for fan assemblies having fan blades with circular arc dovetail roots that mate in circular arc dovetail slots in a disk of a fan rotor.
2. Discussion of the Background Art
A turbofan gas turbine engine used for powering an aircraft in flight includes a fan assembly having a plurality of circumferentially spaced apart fan blades extending radially outwardly from a rotor disk. Ambient airflow is channeled between the blades and pressurized thereby for generating thrust for powering the aircraft in flight. The fan assembly typically includes a plurality of circumferentially spaced apart fan blades each having a dovetail root disposed in a complementary, axially extending dovetail groove or slot in a perimeter or rim of a rotor disk. The dovetail slots are defined by dovetail posts and are complementary in configuration with the blade dovetail roots for radially retaining the blades to the rotor disk. A spacer fills the balance of the space below the blade root within slot.
During a bladeout event, a blade or portion of blade is released and impacts the first trailing blade adjacent the damaged blade causing the first trailing blade to rotate circumferentially. The present invention is particularly useful for fan assemblies with circular arc dovetail roots and slots. This makes the dovetail load up on point locations which jeopardized the integrity of the dovetail. The blade needs to be prevented from rotating too much and loading the corners up. When the blade tends to rotate, the spacer gets pinched between the bottom of the blade root and the bottom of the slot in the disk, thus preventing rotation. The rotational moment is shared by a majority of the pressure face instead of on the corner points of the dovetail root.
The blades are axially retained in the rotor disk to prevent axial movement of the blades in the upstream and downstream directions. Dovetail slots are open at each end due to manufacturing processes used to form the slots. An obstruction is required to prevent the blades from sliding forward or aft in the disks. Typically, a booster spool flange presents a solid ring on the aft side providing an aft obstruction forward retention by a blade retainer. One type of well known blade retainer is disposed in a pair circumferentially oppositely facing retaining slots extending through an adjacent pair of the disk posts. The retainer extends across the dovetail slot so as to axially retain the dovetail roots in the dovetail slots. Also, in the event of a severe event (bladeout, bird ingestion, etc.), the retainer must take additional loads.
A fan disk assembly for a low radius hub design incorporating a circular arc dovetail root and slot to ensure an adequate footprint and load path into the disk has been developed. This design is used for increasing the airflow through the fan blades to increase the thrust without increasing or holding to a limit of a tip of the fan blade. An inner flowpath boundary, often referred to as the hub, is moved radially inwardly from an existing engine design or the engine is originally designed to have, what is referred to as, a low radius hub. Conventionally, a radial transition portion is a transition from a curved blade section at the flowpath to a straight shank at the top of the dovetail. Due to the low inner diameter of the flow path, the radial transition portion of the fan blade from the aerodynamic or curved portion of the blade to the dovetail root is significantly shortened. It is highly desirable to have an improved spacer and retainer for a low radius hub design which incorporates a circular arc dovetail root and slot to ensure adequate blade retention for the first trailing blade adjacent the damaged blade during a bladeout event. It also desirable to provide a spacer and retainer that provide ease of assembly and radially inwardly and outwardly support of the retainer while the spacers are being installed.
A gas turbine engine blade retainer has a block, a retainer slot disposed through the block, and a shelf normal to and extending axially forward of the block below the retainer slot. An exemplary embodiment of the invention further includes a retainer wall depending radially inwardly from the block and the retainer wall has a retainer wall thickness smaller than a block thickness of the block. The shelf is disposed along a radially inner edge of the retainer wall and the retainer slot is disposed through the retainer wall along the shelf. The retainer slot is curved sideways. The retainer slot is arced or curved sideways and may be rectangular in cross-section.
In a particular embodiment of the invention, the retainer slot is rectangular in cross-section, the shelf is a rectangular shelf that is rectangular in cross-section, and the retainer slot is skewed sideways with respect to a shelf centerline extending axially down a middle of the shelf. A radially extending shelf aperture is disposed through the shelf.
In one particular embodiment, the invention is a retainer spacer in a gas turbine engine rotor disk assembly having a number of annular hubs circumscribed about a centerline, each of the hubs connected to a disk rim by a web, and a plurality of circumferentially spaced apart dovetail slots disposed through the rim. The dovetail slots extend circumferentially between disk posts, axially from a forward end to an aft end of the rim, and radially inwardly from a disk outer surface of the rim. A plurality of fan blades have dovetail roots which are disposed in the dovetail slots and blade spacers are disposed in the dovetail slots between a dovetail slot bottom wall and an axially extending root bottom surface of each of the dovetail roots. Pairs of circumferentially oppositely facing retaining slots extend through overhangs of circumferentially adjacent pairs of the disk posts at an axial location where the overhangs begin extending axially forward from the rim, retainers disposed in the pairs of retaining slots. The retainers extend across the dovetail slot so as to axially retain the dovetail roots in the dovetail slots.
A spacer bolt having a spacer bolt head and a threaded spacer bolt shank is disposed through the shelf aperture and a radially extending tab aperture through the spacer tab such that the spacer bolt head engages the shelf. A spacer nut is threadingly secured on the spacer bolt shank such that the spacer nut engages the spacer tab. The retainer slot provides radially inwardly and outwardly support of the spacer tab while the spacers are being installed.